Engines with several cylinders are used in two wheeled motor vehicles and other vehicles. For example, in the case of a V type four cylinder engine, a serially aligned four cylinder engine, and other such engines, the distances between the intake openings of each cylinder are relatively small, and further, the configurations around them vary. In cases where there are differences in intake resistance, a great deal of air may be taken in by some particular intake openings, while the air intake is reduced in quantity for other intake openings. In other words, there are many cases involving an arrangement for the various intake openings in an intake system, when the openings are placed adjacent to each other due to considerations of space or the like, it is quite possible for intake quantity imbalances to arise due to the conformation around the openings and other such factors.
In the design of internal combustion engines, in cases where there are multiple cylinders, it is hard to set out the air intake system circuits in the same manner for each cylinder, so that the aforementioned imbalances in the air intake quantities for each cylinder can easily arise, causing such malfunctions as imbalances in intake volume effectiveness, imbalances in carburetor settings, and the like, to occur. In particular, in the case of the constant vacuum type of carburetor, of the form in which the throttle opening degree is made larger in proportion to the intake quantity, the throttle does not open for cylinders where the intake quantity is small, while the degree of opening for cylinders with a large quantity of intake is great, and the imbalances of intake volume effectiveness, output, carburetor settings, and the like, become all the greater.
For instance, in the case of the structure shown in FIG. 6, with a carburetor base for a four cylinder V type engine where multiple cylinders are arranged front and back, an air cleaner (not shown in the figure) is connected on top of the base 51, and on the lower wall of base 51 there are openings 52a, 52b, 52c, and 52d, made as intake connection openings for the carburetors 52 for each of the cylinders. There are variations in the distances between the outer rim wall area 53 of the base 51 and the various intake connection openings, particularly in the cases of distances to the left and right relative to the rim wall area sides 53a and 53b, and as there is variation in the configurations involved, it is easy for imbalances in intake volume among the various cylinders to occur.